Spotless for imports

[MartinWitt]

Currently, our import ordering in spoon is a bit messy. This leads to an unpleasant time with IntelliJ trying to sort the imports in a more normal order. Why don't we use spotless-maven-plugin to sort all our imports in a fixed sorting? This also helps to reduce diffs in the future for PRs. The benefit compared to checkstyle is that we can do the sorting automatic. See https://github.com/diffplug/spotless/tree/main/plugin-maven#java for an example.

[MartinWitt]

We need to add

          <java>
            <importOrder />
          </java>

Any wishes for the order?
<order>java|javax,org,com,com.diffplug,,\#com.diffplug,\#</order>
<semanticSort>false</semanticSort>
<wildcardsLast>false</wildcardsLast>

[I-Al-Istannen]

I don't care as long as IJ can follow the same order and I don't need to run spotless :^)